1. Field of the Invention
This invention relates to a multilayer composite fabric material comprising a fabric support layer and a composite permselective membrane layer, which is permeable to water vapor, but impermeable to toxic organic vapors. The invention further relates to protective garments fabricated from this material.
2. Description of the Prior Art
There are many situations in modern industrial and military setting where personnel need protection from toxic materials to which they may be exposed, either as an ongoing part of the work environment, or as a result of accident or emergency.
A range of protective garments is now available for use in such hazardous conditions, where the potential or actual release of highly toxic organic vapors and liquids poses a threat to the health and safety of the workforce.
Gear currently used to safeguard workers in these surroundings consists of protective masks, hoods, clothing, gloves and footwear. This equipment, when made from rubber or plastic, can be completely impervious to hazardous chemicals. Unfortunately, these materials are also impervious to air and water vapor, and thus retain body heat, exposing their wearer to heat stress which can build quite rapidly to a dangerous level.
Another approach to protective clothing, well known in the art, is the use of garments manufactured from a laminated fabric incorporating activated carbon, which has the ability to sorb toxic vapors and prevent penetration to the skin. Examples of this method include U.S. Pat. Nos. 3,769,144 to Economy et al., 4,217,386 to Arons et al., 4,433,024 to Eian, 4,513,047 to Leach et al. and 4,565,727 to Giglia et al. The main disadvantage of this approach is that the fabrics lose their sorptive properties with time. As active carbon sites become saturated, the garment becomes unreliable and presents a decontamination problem in addition. In some embodiments it has been shown that the absorption of perspiration from the user can reduce the amount of available carbon to such an extent that the garment becomes unsafe after a use period of only a few hours. Furthermore, these laminates often rely on a layer of polyurethane foam to hold the carbon particles or fibers, a technique which introduces a fire hazard, since some polyurethane foams are highly flammable. The production of these laminates is costly and complex, and the resulting material may have undesirable properties such as flammability, low thermal conduction, and limited life of the polyurethane layer.
Chemical de-activation, using materials treated with reactive decontaminants such as chloroamide, is another possibility, of which U.S. Pat. No. 2,968,675 is a typical example. However, chloroamide-treated fabrics deteriorate over time, necessitating regular inspection and possible reimpregnation. In addition, these fabrics liberate hypochlorite when exposed to perspiration or other moisture, and can cause unacceptable levels of skin irritation to the wearer.
The use of modern semipermeable membranes, as developed for use in the separation of gases or liquids, as a constituent of the protective material is a newer approach which has been exploited to a very limited extent to date. U.S. Pat. No. 4,201,822 to Cowsar discloses a fabric containing known reactive chemical decontaminants, which are encapsulated in microparticles bonded to the fabric. The microparticle walls are permeable to toxic vapors, but impermeable to decontaminants, so that the toxic agents diffuse selectively into the particles, where they are rendered harmless. Encapsulating the active agent in this way avoids the liberation of hypochlorite, and subsequent skin irritation, that has been shown to be a problem with clothing treated with chloroamide. Employing a similar concept, U.S. Pat. No. 4,460,641 to Barer et al., discloses the use of microporous hollow fibers, whose lumina are filled with one or more chemical neutralizing agents, to form one layer of a protective fabric. Of course in both these cases, the decontaminant agent will still become exhausted with time.
The deployment of a synthetic polymeric membrane as a barrier to the permeation of organic vapors, rather than as a means of absorption, is disclosed for example in U.S. Pat. Nos. 4,469,744 and 4,518,650 to Grot et al., and 4,515,761 to Plotzker, all assigned to DuPont. In these patents, the ability of the composite fabric to reject toxic organic agents resides in a layer of semipermeable highly fluorinated ion exchange polymer, which is permeable to water vapor, but relatively impermeable to a broad range of organic vapors. In this way, the user can remain cool and comfortable, but enjoys protection from harmful agents. The main disadvantage of these garments is in the measure of their impermeability. While they are adequate for protection in many industrial applications, their organic vapor transmission rates depend on the molecular weight of the substance involved, and may be far in excess of recommended safe exposure levels for potent toxic agents with low molecular weights.
Thus there still exists a very real demand for improved protective clothing that can offer acceptable levels of impermeability to highly toxic organic vapors of low molecular weight, while minimizing the discomfort and heat stress that accompanies the use of conventional rubber or plastic protective suits. The protective fabric material of the present invention represents a novel application of the technology of multilayer composite membranes to the solution of this problem, and provides a material suitable for fabrication into garments with superior toxic vapor rejection characteristics, combined with good water vapor transmission properties.